In recent years there has been an increasing need for composite materials having high fracture toughness, hardness and wear resistance for use in cutting tools, wear parts, and structural applications such as dies, turbines, nozzles, and the like. Due to their high modulus of elasticity, high hardness, and high strength, single crystal whiskers of such materials as carbides or nitrides of titanium, zirconium, hafnium, niobium, tantalum, and tungsten could present attractive materials for composite technology. However, prior to the present invention, methods for producing such whiskers in commercial quantities have not been known. Known laboratory methods for producing whiskers of metal carbides or nitrides, for example, titanium carbide, involve placing a substrate material suitable for whisker growth, for example a graphite or mullite plate or tube, at the center of a quartz tube, and heating the substrate to a temperature suitable for whisker growth. Typical temperatures in such reactors range from about 800.degree.-1400.degree. C. The reactor tube is flushed with hydrogen, and reactant gases, typically in a molar ratio of carbon or nitrogen to metal of about 1:1, are flowed through the heated reactor to form whiskers on the substrate. The prior art processes have presented the disadvantages of decomposition of reactants subjected to extreme temperatures before reaching the substrate material, lack of control of whisker morphology and dimensions, and limitations on the efficiency of whisker production by such methods.